Have you heard that, since believers in Christ are “grafted in” to Israel, all believers must observe the Law given to Israel? This may include twisting things to say that you, yes you, are a real, physical descendant of Israel through the lost tribes of the northern kingdom of Israel.
Whether they say this part or not, this one text is made to carry quite a lot of weight in seeking to convince people to be Torah observant. Does it Romans 11 really teach all this, or are we who have encountered this argument simply encountering the same kind of mindset that sees papal infallibility in every nice thing said of Peter, or immaculate conception in every nice thing said of Mary?